1. Field of the Invention
This invention pertains generally to treatment of tumors and benign tissues using thermal therapy, and more particularly to a method and apparatus for applying interstitial hyperthermia, simultaneous thermoradiotherapy, simultaneous thermobrachytherapy, or thermal ablation for the treatment of cancer or benign diseases.
2. Description of the Background Art
Localized hyperthermia may be used as an adjuvant to radiation treatment and chemotherapy in the clinical management of cancer. Traditionally, heat and radiation have been applied sequentially (hyperthermia immediately pre/post radiotherapy), using special applicators to apply heat-inducing energy within a tumor, raising the temperature to approximately 42.5.degree. to 45.degree. C., and maintaining the temperature for approximately 30 to 60 minutes. Recent biological studies and clinical evidence, however, have indicated a significant enhancement of combined therapy if applied concurrently over a longer duration. This form of therapy would be most applicable to interstitial therapy where the catheters are implanted directly within the tissues to be treated, thereby localizing the heat and radiation within the target tissue and reducing normal tissue toxicity.
Interstitial heating remains a treatment of choice for many tumors, despite the invasive nature of the technique, since the heating and/or radiation sources are inserted directly into the tumor, thereby localizing heat within the target volume and sparing more of the surrounding normal tissue. These methods are most often used for treating bulky or unresectable deep-seated tumors surrounded by sensitive normal tissues (i.e. brain, neck), or for sites in the pelvis (i.e. prostate, cervix) which are difficult to localize by external methods. The implant catheters are inserted intraoperatively often using pre-planned trajectories that are determined primarily for the radiation dose patterns. The number and location of heat sources are dictated by the tumor geometry and the power deposition or heating capability of each source, and the remaining catheter tracks are generally used for thermometry measurements. Interstitial thermotherapy has traditionally been given "sequentially" to brachytherapy, with heating procedures performed immediately prior to insertion of the radioactive sources and after removal.
There are many interstitial heating technologies being used clinically or currently under development. Typically, interstitial techniques utilize the same catheters or needles for both heating and radiotherapy, but most of the technology is not amenable to concurrent insertion of radiation sources during thermal therapy. Conventional heating technologies employed for "sequential" interstitial thermal therapy include radiofrequency local current field (RF-LCF) electrodes, capacitively coupled RF electrodes, coaxial cable mounted microwave antennas, inductively heated ferromagnetic seeds, resistance wire, fiber-optic coupled lasers, and hot water tubes. Two techniques, however, have been adapted successfully for simultaneous therapy: (i) RF-LCF current heating, and (ii) use of conductive heating catheters.
RF-LCF heating devices use metal implant needles with electrical connections directly from the template, leaving the lumen available for simultaneous insertion of radiation sources, but require that a portion of the implant needles be designated for thermometry measurements. The RF-LCF approach has been shown to be efficacious in many clinical situations, but the heating dependence on needle alignment, appropriate needle pairing, and the inability to adjust the longitudinal heating pattern dictate that alternative techniques be investigated. In partial response to this need, it has been proposed to use alternating segmented RF electrodes (which are not compatible with insertion of radiation sources) with standard needles within the same implant array to improve longitudinal control.
Recent designs of open lumen conductive heating catheters, wherein transducers are placed within a brachytherapy implant catheter and surrounded by a coupling fluid, having multiple resistance-wire heating elements and built-in temperature sensing are being developed for concurrent therapy, but have not yet been implemented in the clinic. These conductive heating catheters have the potential for longitudinal control of heating but, since there is no power deposition in tissue, the use of these catheters is limited to clinical situations allowing for dense implant spacing (1 to 1.5 cm, large number of heat applicators) and lower per fusion targets. However, an attractive feature of this conductive technique is the possibility of parameter estimation in order to estimate minimum tumor temperatures for treatment control purposes.
Although efficacious in many clinical situations, none of the aforementioned methods and devices allow the power deposition to be easily varied along the length of the implant during the course of treatment to account for heterogeneities in tumor structure and dynamic changes in blood perfusion. Existing technologies require that the heating catheters be closely spaced, and are generally sensitive to the alignment and interaction of neighboring sources. This increases the number of catheters or needles which must be implanted for acceptable uniformity of heating, leaving few for temperature monitoring and control of the treatment. Further, the ability to improve control and penetration of the power deposition of interstitial applicators is a critical problem: in order to offer the best chances for a good clinical response, the whole tumor and tumor margins must be heated to therapeutic levels, with a steep transition to lower temperatures in the surrounding normal tissue. This criteria, combined with the often heterogeneous nature of the target tissue, dictate that control and penetration be improved. Recent efforts to improve control of the power deposition along the length include technology developments such as segmented RF electrodes and conductive sources. Special pre-wired implant templates and hardware/software configurations expedite treatment setup and allow for multiple needle activation schemes are offering improvement in control of the RF-LCF heating. In addition, the strategy of cooling the source surface to improve the radial heating distributions has been investigated for RF-LCF and microwave sources.
Accordingly, there is a need for a direct-coupled interstitial ultrasound applicator for the simultaneous delivery of hyperthermia and radiation therapy which provides for variable power deposition and accurate treatment control. The present invention, satisfies that need, as well as others, and overcomes the deficiencies in prior methods and devices.